This invention relates generally to electrochemical energy sources and, more particularly, to battery assemblies capable of retaining electrochemical energy in a reserve state until activation.
In the use of systems requiring a main battery for electrical requirements, the retention and use of a back-up battery to provide for power upon failure of the main battery is highly preferred. Back-up automobile batteries, for example, are known to provide a backup source of power in the event of battery failure due to accidental discharge (such as leaving the lights on), battery malfunction (such as internal shorting), and battery limitations (such as weakness in extreme cold). A variety of back-up batteries have been designed, each with its own characteristics and limitations.
A main battery for an automobile is usually of the lead-acid type. A lead-acid battery provides a recharge capability superior to most battery types. It does not have a high specific or volumetric energy density, however, and necessarily must be a large and heavy battery. While a second lead-acid battery could be carried in an automobile to serve as a backup for the first, this solution is not generally practical for reasons of cost, space, weight, and limited shelf life without a recharge.
A back-up battery must provide adequate voltage and power levels to either replace or recharge the main battery for a limited period of time. Because the immediate need to use a back-up battery is not predictable, the back-up battery should have a long shelf life. Storage conditions of a back-up battery may vary, and therefore durability and safety are principal concerns. This is particularly true when the back-up battery contains more dangerous electrolyte fluids. Thus, it is preferable that the back-up battery be small, lightweight, durable, and not contain dangerous fluids. It is further desirable that the back-up battery be convenient to use in a variety of main battery failure scenarios. Furthermore, a preferable back-up battery should be inexpensive, and environmentally safe.
It is known that nickel-cadmium (NiCad), rechargeable back-up batteries, with jumper cable clips attached and stored in separate hinged-door compartments, are available for charging depleted batteries, powering portable television sets and radios, and the like. Such devices, while providing for short-term, portable power needs, do not have significant shelf life or power. They require frequent recharging, and eventually suffer performance degradation from that recharging.
In order to extend shelf life, back-up batteries have been designed as reserve electrochemical batteries for recharging main batteries. In a reserve battery, the electrolyte is stored separate from one or both types of electrodes, providing for an extended period of shelf life. Significant degradation of the electrodes generally does not occur until the reserve battery is activated by introducing electrolyte to the electrodes.
Nevertheless, whether reserve or not, back-up battery designs must trade off charging power level against the preference for reduced size, weight, cost, and safety concerns. Compact back-up batteries for automobiles have therefore been designed for slowly recharging a main battery rather than replacing it or jump-starting the automobile engine directly. An exemplary device is shown in U.S. Pat. No. 4,794,058, to Theiss. The Theiss device includes an ammeter for observing the progress of the charge, an expandable bag to store the electrolyte under pressure, and a frangible trigger member for activating the battery (i.e., conveying the electrolyte to the electrodes). Such a device, while conveniently small, would be expensive to manufacture due to its many intricate and expensive components (e.g., charge control circuitry and complex activation system). Furthermore, it is inconvenient to use, in that it takes an extended period of time to charge the battery. The user of the battery (e.g., the motorist) must wait patiently to regain the use of the main battery. Furthermore, such a battery does not provide assistance when the main battery is no longer capable of holding an adequate charge, such as when it is shorted out internally, or when it is significantly degraded, and at a very low temperature.
While the Theiss device uses a pressure feed system (the elastic bag) to deliver the electrolyte to the electrodes, other systems are also known. A spring-feed system is disclosed in U.S. Pat. No. 3,894,888, to Gold. A system driven by a tube of compressed gas is disclosed in U.S. Pat. No. 4,695,520, to Koper et al. Gravity-feed systems are also known in the art. U.S. Pat. No. 3,953,239, to Anderson, discloses a reserve battery comprising aluminum alloy and silver oxide electrodes and a pre-heated potassium hydroxide electrolyte.
Accordingly, there has existed a definite need for a back-up battery providing adequate voltage and power levels to replace a main battery for a limited period of time, and its related method of use. The back-up battery should have a long shelf life, high durability, and it should have a minimal risk of leaking dangerous chemicals. The back-up battery should be small, lightweight, and convenient to use in a variety of main battery failure scenarios. Furthermore, the back-up battery should be inexpensive, and environmentally safe. The present invention satisfies these and other needs, and provides further related advantages.